A user of a firearm such as a rifle or carbine may sometimes inadvertently drop or intentionally force the firearm to the ground (such as to clear a jammed firearm mechanism), and, for this reason, drop strength is an important factor in the development of firearms. With advances in polymeric materials being used in, for example, carbine stocks, manufacturers have the ability to provide users with relatively lightweight firearms, even in those having adjustable stocks.
Adjustable stocks generally have a housing and a lever that can be disengaged or pivoted, so as to allow a locking pin to engage the carbine buffer tube (or receiver extension) at various points along the tube. That is, the locking pin may move into and out of a number of holes in the extension tube so as to enable adjustment of the length of pull. In doing so, the locking pin may also travel through or within a hole placed in the housing of the stock.
However, when the stock/firearm is dropped, the impact may cause the polymeric housing to break completely, or deform (such as at the hole through which the locking pin passes) in a manner that prevents the stock from being adjusted again. For example, the impact may cause the locking pin to deform the hole such that the hole in the housing can no longer accept the pin, and/or the deformed hole may allow the locking pin to shift, becoming stuck, or otherwise unable to properly travel in a direction transverse to the holes in the buffer tube.
In some cases, when the stock/firearm is dropped, the locking pin, which may be steel, may exert enough load to the buffer tube, which may be aluminum, to cause the hole in the buffer tube to deform. If the locking pin itself also bends or shifts, the damage may be exaggerated, and thereby allow the locking pin to dive and disengage (also known as auto-collapse).
In some cases, when the stock/firearm is dropped, the locking pin itself may bend under load and causes jams. This may happen either as the lone failure mechanism, or in conjunction with deformation of the housing and/or the hole in the buffer tube, as described above.
All three of the failure modes described above may occur independently or in conjunction.
Therefore, there remains a need for a lightweight firearm stock with an improved drop strength, and/or other new and innovative features.